1. Field of the Invention
The present invention relates generally to power factor correction circuits, and more particularly to a power factor corrector which uses a high frequency current mode regulator integrated circuit to provide peak current limiting at a high frequency rate on a cycle by cycle basis. Input power line isolation is obtained with output direct current voltages that can be desirably less than the rectified input voltage.
2. Description of the Prior Art
Power factor correction circuits are known in the art. For example a UC3852 circuit manufactured by Unitrode Corporation and described in its "Products and Applications" handbook for 1995 and 1996 on pages 10-269 to 10-284. Such a circuit utilizes a full wave rectified input signal such as is shown in FIG. 1 as curve 10.
Cycling from point A to B to C to D to E to F to G etc. This signal is applied across an inductance/capacitance circuit so that the capacitor, which produces the output voltage, is charged up during the time from point A to point B at which point the current decays to point J where it is then further charged to point D. This charging/decaying curve continues to point K to point F to point L etc. to provide a ripple curve of a substantially DC voltage for use by the down stream equipment. However, using this as an input signal, and without power factor correction, the input current would lead the input voltage to produce a power factor of about 0.85. This shows that only about 85% of the output signal is driven from the input signal thus producing a power factor of about 0.85. Increasing the width under curve 10 between points J and D; and between Points K and F would increase the power factor. However, increasing the area under these points would bring point J down curve 10 towards point C and point K down the curve towards point E which would badly increase the amount of ripple in the output voltage.
Utilizing a power factor correction circuit such as the above mentioned UC3852, the power factor can be corrected to 0.998 and thus, the output signal is driven by the line input during nearly 100% of the time.
One disadvantage to circuits such as the UC3852 is that the DC output circuit is not isolated from the AC input circuit which could produce a short circuit if a diode rectifier were used at the input. Another disadvantage for circuits such as the UC3852, is that the output voltage is considerably higher than the input voltage and, in fact, may be more than twice as high. This increased output voltage is undesirable for many situations such as, for example, supplying power to aircraft components because most aircraft use a 115 volt AC source and a 28 volt DC source. Accordingly, the output of the power factor correction circuit using the UC3852 could be as high as 230 DC volts when it would be desirable for the output to be a little higher than 28 volts.